Wireshark-dev: [Wireshark-dev] What kind of L7 protocols are dissected based on content identification?

From: 王睿思 <wangruisijdg@xxxxxxxxx>
Date: Mon, 2 Mar 2009 16:46:17 +0800

Hello:
    I have reading the source code for days, and still I can't
distinguish the L7 protocols between the port identified and content
identified.
   for example: supposing an  packet used the protocols:
"IP-TCP-RTSP",  but when dissect how can the dissect_tcp() find its
subdissector is dissect_rtsp(), did it's based port identification or
content identification?
  Besides, is there any method to know the data type in the
application layer?（e.g. if we could find the payload of RTSP is audio
or video and so on）
Some one could, please, tell me ?

Best regards,

 Kathryn